The Pavlovian conditioning situation is described by a set of operations in which a "conditional stimulus" (CS) is paired a number of times with an "unconditional stimulus" (UCS). The CS is said to be "neutral", i.e., it elicits little relevant activity prior to its pairing with the UCS. As the name implies, the UCS is selected because it elicits relevant activities from the outset--unconditionally--prior to any pairings. In Pavlov's well-known conditioning work, the CS was (for example) a bell, and the UCS was food, which elicited a conveniently monitored salivary response. Pavlov suggested that the usual drug administration procedure was operationally similar to this paradigm, with the CS being the preparations for drug administration (which preceed the systemic stimulation induced by the drug), with the actual pharmacological assault constituting the UCS. A great deal of research, primarily from Russian and Eastern European laboratories, indicates that many visceral responses can be modified with pharmacological conditioning procedures. Recent research from the PI's laboratory suggests that a psychopharmacology of drug action must include not only the central effects of a drug, but also those conditional responses (CRs) evidenced in anticipation of these central effects. It is suggested that these anticipatory pharmacological CRs frequently attenuate the effect of a drug (thereby producing "tolerance"), and many tolerance phenomena can only be understood from a Pavlovian learning perspective. The proposed research will assess the contribution of drug CRs to the observed effects of repeated administrations of a variety of narcotics (especially opiates) in the rat. The research has implications for the role of the drug administration ritual in drug abuse.